Linux, the poster child for open source software, was officially disclosed by Linus Torvalds in a Usenet newsgroup posting on 25 August 1991.
The two decades since have seen it expand from a personal pet project to a platform capable of running on everything from mobile phones to web servers and even mainframes, with no sign of it running out of steam just yet.
Thanks to its close similarity to Unix, Linux has developed into an excellent platform for users requiring Unix-like levels of reliability. Consequently, Linux distributions have gradually displaced many of the ageing proprietary Unix flavours for high-end workstation and server applications.
At the same time, Linux now powers many of the world's supercomputers, and underpins a number of embedded and mobile platforms, notably Google's Android and HP/Palm's webOS.
All of this means that Linux is just as pervasive as Microsoft's Windows, although perhaps not as visible. While Windows dominates on desktops and laptops, Linux is more often powering the infrastructure rather than something that end users interact with directly.
Strictly speaking, the Linux label refers only to the operating system kernel, but is commonly used to describe packaged distributions such as those from Red Hat or Suse which integrate numerous other open source modules (such as the KDE or Gnome desktops) to build a complete, functioning operating system.
Much of the strength of Linux stems from its community-driven, collaborative development model, and Torvalds's decision to release his new brainchild under the GNU General Public Licence, which permits the software to be used without restriction.
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